1. Field of the Invention
The present invention relates to an automated warehouse having high space utilization efficiency and high floor surface utilization efficiency and a management method therefor.
2. Description of the Related Art
Conventional production plants widely use computer-controlled automated warehouses to store and manage loaded stock objects such as products, parts, and materials and output them, as needed. Such automated warehouse can be roughly classified into unmanned automated warehouses such as stacker crane type automated warehouses and manned automated warehouses such as forklift type automated warehouses.
As shown in the plan view of FIG. 1, in general, in an unmanned automated warehouse 1 of the former type, racks 3 having storing spaces 2 arranged in rows and columns are installed on the two sides of the traveling path of a stacker crane 4, the stacker crane 4 travels in the space between the racks along a rail 5, and a fork unit 6 moves up and down in the stacker crane 4. In a loading area 7, when the stacker crane 4 having a stock object placed on the fork unit 6 moves. horizontally, and the fork unit 6 moves vertically to convey it to the target storing space 2, the fork unit 6 is driven in the horizontal direction to load the stock object in the target storing space 2. In contrast to this, when a stock object is to be unloaded, the fork unit 6 moves to the target storing space 2, picks the stock object from the storing space 2, and conveys it to an unloading area 8.
In a manned automated warehouse of the latter type, an operator drives and operates a forklift to store stock objects placed on a pallet in a target storing space of a rack, together with the pallet, or picks stock objects on a pallet from a storing space, and conveys them to an unloading area.
The former automated warehouse and the latter automated warehouse differ in that the former is unmanned, and the latter is manned. However, they have the following many common points.
(a) Stock objects are stored in racks partitioned into storing spaces in rows and columns (in the form of a matrix) PA1 (b) Stock objects are translated to be loaded/unloaded into/from storing spaces. PA1 (c) A space for allowing loading/unloading means such as a stacker crane and forklift to move and operate is required on the floor surface. PA1 (d) Racks must be arranged to allow a stacker crane or forklift to approach. PA1 (e) In loading/unloading operation, stock objects placed on a pallet and stock objects stored in a storing case are handled.
In either of the conventional automated warehouses, however, since racks are partitioned in the form of a matrix to arrange storing spaces in rows and columns, members constituting the racks, spaces for partitioning members between storing spaces, spaces for pallets and storing cases, and available spaces (marginal gaps) for loading/unloading operation are required. Each storing space occupies a wide space as compared with the size of a stock object, and the outer dimensions of each rack are large.
In addition, storing spaces formed in each rack tend to have a uniform size in consideration of the formation and operation of racks. For this reason, each storing space has a size corresponding to the size of a largest stock object. When a general stock object or small stock object is stored in a storing space, a wasteful space is produced in the storing space. The storing spaces cannot therefore be fully utilized depending on the type of stock objects. In many cases, the ratio of the area occupied by a rack to the area occupied by all the stock objects is less than 50%. That is, the storage efficiency is low when racks are used.
More specifically, FIG. 2A shows the rack 3 in which largest stock objects 10A placed on a pallet 9 and a general stock object 10B on a pallet 9 are stored in storing spaces 2. FIG. 2B shows a comparison between the area occupied by the stock objects 10A and 10B collected at a corner and the area occupied by the rack 3. FIGS. 2A and 2B show how much an extra rack-occupying area is required as compared with the sizes of the stock objects 10A and 10B. In consideration of a volume ratio in this state, it is obvious that the space efficiency and volume efficiency of the automated warehouse are low when multistage racks are used.
In addition, when multistage racks are used, stock objects are loaded/unloaded into/from storing spaces by translating the stock objects from the front surfaces of the racks by using a fork unit or the like. For this reason, a space for allowing a stacker crane, forklift, or the like which is used for loading/unloading operation to travel must be ensured on the floor surface. Furthermore, the layout of an automated warehouse is limited such that two or more racks cannot be arranged in contact with each other, because a loading/unloading means such as a fork unit must access the racks. As a consequence, the ratio of the area occupied by the storing spaces to the floor surface in the automated warehouse is low, and hence the storage efficiency is low. In some case wherein a forklift is used, in particular, the floor surface area in which the forklift travels becomes larger than the floor surface area of storing racks.
In loading/unloading operation using pallets, one pallet on which many stock objects can be stacked is the operation unit. However, the number of stock objects requested to be unloaded rarely coincides with the number of stock objects placed on one pallet. For this reason, when an unload request is generated, a pallet is conveyed to a picking position in an unloading area, stock objects are picked from the pallet by the required number, and the remaining stock objects are loaded into the original storing space, together with the pallet. This tends to demand extra loading/unloading operation. In addition, the operator often picks stock objects by operating a balancer or the like, posing problems in terms of operation efficiency and safety.
According to Japanese Patent Laid-Open No. 6-115608, a trolley that travels along a ceiling is prepared above a stocking area, and a stock object is held with a container hoisting attachment prepared below the trolley. With this structure, a stock object can be conveyed to an arbitrary place in the stocking area or unloaded from the stocking area. According to this automated warehouse, since no space for allowing the trolley to travel is required on the floor surface in the stocking area, a wide stocking area can be used.
In this conventional automated warehouse, however, since the container hoisting attachment is suspended from the trolley with a wire (winding rope), when the trolley travels while a stock object is held with the container hoisting attachment, the stock object rolls. Even after the trolley is stopped, the stock object rolls. This makes it difficult to place the stock object at an accurate position. For his reason, when a stock object is stacked on another stock object by lowering the container hoisting attachment, a load of stock objects may fall because of a positional shift of the stock object.
When the stock object held with the container hoisting attachment rolls, the stock object may collide with another stock object stacked at a position near the position where the held stock object is to be placed. For this reason, a considerably large interval must be ensured between stock objects stacked in the stocking area. As a consequence, the stock object storage efficiency of the stocking area is degraded.
A production line for various types of tires with various sizes requires an assorting unit for randomly conveying the various types of tires with the various sizes manufactured in the previous process to the next process.
FIG. 13 is a perspective view showing an example of a conventional tire sorting unit. Referring to FIG. 13, various types of tires with various sizes manufactured in the previous process are placed on loading conveyors 102 and 103 and conveyed in the direction indicted by the arrows, and tires 35 are sorted according to types by assorting units 106 and 107 installed at the junction of branch conveyors 104 and 105. As a result, the tires are stacked on each other on branch conveyors 104a to 104g and 105a to 105g by a stacking unit. After the tires in this state are respectively conveyed to unloading conveyors 110 and 111 in the center, the tires in a stacked state are transferred into an empty unit 109 set in a transfer unit 220 in advance, thus obtaining a tire-loaded pallet 130. Thereafter, the pallet is conveyed downstream on a loading conveyor 123. The tire-loaded pallet 130 is conveyed to the next step by a truck or forklift.
As described above, according to the conventional tire sorting unit, for example, to select and convey seven types of tires, seven branch conveyors are prepared. In order to handle more types of tires with more sizes, branch conveyors must be added, resulting in increases in cost and installation area.
In consideration of the total time of the time required to stack tires on each other on branch conveyors, wait time, and the time required to convey tires on the conveyors, a long period of time is required to obtain a tire-loaded pallet. According to Japanese Patent Laid-Open No. 06-312838, a tire transfer unit has been proposed. In this unit, a tire storing place constituted by a plurality of tire storing conveyors arranged side by side and tire conveyance between the tire storing place and loading/unloading tracks are mechanized. In this proposal as well, conveyors are required for the respective types of tires.